Cathodes for electron discharge devices



D. MacNAlR 2,810,090

CATHODES FOR ELECTRON DISCHARGE DEVICES 3 Sheets-Sheet 1 Oct. 15, 1957Filed June 15, 1953 lNl ENTOR 0. MAC NAIR BY W ATTORNEY ANODE CURRENT IIN AMPERES/C114 Oct. 15,1957 MaONAIR 2,810,090

CATHODES FOR ELECTRON DISCHARGE DEVICES Filed June 15, 1953 v 3sheets-sheet 2 FIG. 3

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CATHODES FOR ELECTRON DISCHARGE DEVICES Filed June 15, 1953 3Sheets-Sheet 5 FIG-4 LOO 2O 4O 80 I 20 I60 200 240 A NODE PO TENT/A L EIN VOLTS m/vsn/ron 0.- MAC NAIR Bl g5.

ATTORNEY cArnonEs ron ELECTRON DISCHARGE nnvrcns Donald MacNair,Berkeley Heights, J., assignor t Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationJune 15, 1953, Serial No. 361,663

Claims. (Cl. 313-339) This invention relates to electron dischargedevices and more particularly to such devices including cathodes of thetype disclosed inmy applications Serial Nos. 361,527 and 361,263 filedJune 15, 1953.

As disclosed in detail in the applications above identified. extremelyhigh current densities and perveances are realizable with thermioniccathodes of the general construction wherein an electron emissivecoating is provided upon the inner wall of a hollow body, the cavity inthe body being substantially completely enclosed except for an aperturefor egress of the electron emission from the coating.

One general object of this invention is to realize improved performancecharacteristics for hollow cathodes of the general character abovenoted. Another, and more specific, object of this invention is to enableattainment of unique and eminently advantageous emission and operatingcharacteristics for such cathodes. More specifically, it is an object ofthis invention to obtain a plurality of individually controllable highdensity electron beams from a single hollow cathode.

The present invention is predicated in part upon the discovery thatunique operating characteristics are attainable with devices includinghollow cathodes having a plurality of apertures therein and one or moreelectrodes each in electron controlling or electron receiving relationwith a corresponding one of the apertures.

Thus, in accordance with one broad feature of this invention, in anelectron discharge device having a hollow cathode, the cathode isprovided with a plurality of apertures, whereby a plurality ofindividual electron beams are produced, and a plurality of electrodeseach in cooperative relation with a respective aperture.

In accordance with a more specific feature of this invention, a deviceof the general construction above described comprises a plurality ofanodes each opposite or aligned with a respective aperture in thecathode and means are provided for controlling the intensity oftheelectron stream to any one or all of the anodes. It has been found that,despite the fact that the source of the electron streams is the same forall, the intensity of each stream can be varied over a wide rangewithout significant alteration in any of the other streams.

In one specific embodiment, the inner surface of the cathode is definedby a hemispherical wall and a substantially plane wall extending acrossthe base of the hemispherical wall and having a group of aperturestherein.

In another specific embodiment, the cathode is in the form of a hollowcylinder, closed at its ends and the cylindrical wall is provided with aplurality of apertures, equal in number'to the number of electronstreams or beams desired.

The invention and the above-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing, in which:

Fig. 1 is an elevational view partly in section and rates Patent2,810,090 Patented Oct. 15, 1957 Fig. 2 is a plan view of the cathodeand heater assembly of the device depicted in Fig. 1;

Fig. 3 is a graphical representation of the electron emissioncharacteristics of the cathode in Fig. 2;

Fig. 4 is a graphical representation of the relationship between theemission characteristics of individual electron emitting orifices of thecathode in Fig. 2;

Fig. 5 is a longitudinal sectional view of a cylindrical hollow cathodein accordance with this invention;

Fig. 6 is a partial section view of another embodiment of this inventionwith portions broken away for clarity; and

Fig. 7 is a longitudinal sectional view of an electron discharge devicein accordance with this invention.

Referring now to Fig. 1, an electron discharge device may be seencomprising a highly evacuated envelope 10 which contains a hollow body11 including a cavity 12. The internal surface of body 11 definingcavity 12 is covered with a coating 13 of electron emissive material,for example a mixture of the oxides of barium, strontium and calcium.Communicating between cavity 12 and the exterior of body 11 are aplurality of orifices or apertures 16, 17 and 18. A heater 20 comprisesa series of turns of resistance wire about body 11 and a heater shield21 encompasses both body 11 and heater 20'. The ends of the heater 20are connected via lead wires 22 and 23 to a battery 30.

A series of electrically independent anodes 26, 27 and 28 are positionedeach opposite a respective orifice 16, 17 or 18 of body 11. The anodes26, 27 and 28 are each connected to an independent plate supply voltageand the body 11 is grounded through its lead 24. For purpose ofillustration, apertures 16, 17 and 18 are shown arranged in a singleline as are anodes 26, 27 and 28. The arrangement of the apertures alongwith its respective anode may be varied without departing from the scopeof this invention. Each anode 26, 27 and 28 is in position to receivethe high intensity electron stream emerging from its respective apertureand passing through the intervening space to the anode, withoutaffecting either the other electron streams oranodes.

In Fig. 2, which is a plan view of the cathode of Fig. 1, the front faceof body 11 including aligned orifices 16, 17 and 18 is shown. Portionsof coating 13 may be seen through each of the apertures and thepositions of anodes 26, 27 and 28 are shown by dotted lines encom--passing the apertures. As was described in my applications citedheretofore, high intensity continuous electron beams in the order of 1to 5 amperes per square centimeter are produced from hollow cathodesupon which the electron emissive coating is located on the surfacebounding an internal cavity as opposed to a maximum continuous emissionof approximately 500 milliamperes for a conventional oxide coatedcathode. Cathodes of this invention obtain such high emission, forexample, in a hollow cylinder as shown in Fig. 2 including threeorifices 0.020 inch in diameter producing an electron beam from eachorifice of one ampere per square centimeter of orifice size with eachanode at a potential of approximately volts. The total emission fromthis cathode is, therefore, three amperes per square centimeter, Whichis an increase of sixfold over emission of conventional oxide coatedcathodes. Emission from each individual orifice is greater by a factorof two than emis sion of conventional oxide coated cathodes.

Fig. 3 represents graphically the electron emission of the threeapertures of the device of Fig. 1 when the same variable potential isapplied to the anodes 26, 27 and 28.

. The emission characteristic curves are nearly superimposed. Anydifferences noted are attributed to such factors as variations inorifice size, individual anode potential, and limitations upon theaccuracy of measurement of anode current.

Over and above the high beam intensity obtained from this form of hollowcathode, the beam intensity from each orifice is substantiallyindependent of potential or changes in potential of the anodesassociated with each of the other orifices. This characteristic isclearly shown in Fig. 4 wherein a constant potential of 50 volts wasmaintained upon the anodes 26 and 27 while the potential of anode 28 wasvaried over the range from zero to 200 volts. Emission from orifice 18,designated as Ib3, varied over this range by a factor of fifteen showingan emission characteristic illustrated above in Fig. 3. The emission oforifices 16 and 17, In and I192, respectively, subject to the constantpotential of their respective anodes remained substantially constant ata value in the order of 0.5 ampere per square centimeter. For allintents and purposes, the emission from orifices l6 and 17 is completelyindependent of emission from orifice 18 and the field established byanode 28.

Thus, in accordance with this feature of the invention, a single hollowcathode may be utilized to produce a plurality of high intensityelectron beams each of which is independently controllable, and theefiect upon a single beam of control of adjacent electron beams isnegligible upon its emission. This structure finds application as areplacement for a plurality of individual cathodes in multiple electronbeam devices resulting in a notable simplification in design and areduction in heater power required as well as enhanced cathode emission.

Another embodiment of this invention is shown in Fig. comprising ahollow cylindrical tube or body 51, the ends of which are closed. Theinternal surface of body 51 defines a cavity 52 and that surface iscovered with a coating 53 of electron emissive material. Along thecylindrical walls of body 51 are a series of apertures 54. A tubularanode 55 encompasses body 51 in position to receive electrons emittedfrom the tube 51 through apertures 54. A hairpin type heater 56 extendsthrough the interior of tube 51 and is insulated therefrom by bushings57. The cathode of this embodiment includes a large electron emissivesurface bounding a cavity within the hollow body. A plurality ofapertures allows egress of electrons emitted from the coating 52.. Thecoating itself is substantially completely shielded from positive ionbombardment from the anode. This embodi ment obtains the high intensityelectron emission of the hollow cathode in a form particularly adaptedfor use in cylindrical or flattened tubular electrode structures and,particularly, beam power vacuum tubes.

Referring now to Fig. 6, another embodiment of this invention may beseen comprising a hemispherical body 61 defining cavity 62 bounded by aninternal surface of body 61 which is covered with a coating 63 ofelectron emissive material. Body 61 includes a planar wall in which theplurality of apertures or orifices 64 are positioned. An anode 65 ismounted in spaced relationship from the planar wall of body 61 inposition to receive electron emission through orifices 64. In thisparticular embodiment the major portion of emissive coating ispositioned upon a hemispherical surface bounding the cavity within body61. The planar anode may be positioned at a substantially uniformdistance from the orifices in the hollow body 61 despite the sphericalconfiguration of the majority of the coating 63 of electron emissivematerial.

In Fig. 7 a hollow cathode may be seen including a plurality of electronemitting orifices or apertures from which an anode receives electronemission and a modulating electrode interposed between the orifice andthe anode. In that embodiment, body 71 defines cavity 72 bounded by aninternal surface of body 71 upon which a coating 73 of electron emissivematerial is positioned. A series of apertures 74 extend across one faceof the body 71. Opposite the aperture 74 an anode 76 is mounted andinterposed between the orifices 74 and anode 76 is a modulatingelectrode 75 which, for example, may comprise a mesh grid or, as shown,a plate perforated to match orifices 74. The modulating electrode is sopositioned that openings therein correspond to orifices 74 and theelectron beam emitted from orifices 74 is, therefore, not dissipated toany appreciable extent by striking the modulating electrode 75.

As is taught in my application Serial No. 361,527 mentioned heretofore,the configuration of an electron beam emitted from a hollow cathode canbe controlled and, in particular, the size of the beam is substantiallythat of the emitting orifice. Under such conditions the openings inmodulating electrode 75 may correspond in size to the size of orifices74 to control the electron beam. Since a single anode and singlemodulating electrode are shown in connection with this embodiment, theanode current depends upon the total emission obtained from all of theapertures 74 and the effect of modulating electrode 75. To obtain aplurality of independently controllable electron beams, an individualanode and modulating electrode for each orifice may be substituted forthe electrodes 76 and 75 respectively.

It is to be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

1. An electron discharge device comprising a highly evacuated envelope,a conducting body within said envelope having a cavity therein, acoating of electron emissive material upon the interior surface of saidbody bounding said cavity, said body being closed except for a pluralityof distinct electron emission apertures communicating between the cavityand the exterior of said body, means for heating said body, andindividual electron accelerating means within said envelope eachpositioned adjacent a respective aperture.

2. A multiple electron beam discharge device comprising a highlyevacuated envelope, a conducting body Within said envelope, said bodyincluding an internal surface defining a cavity therein and being closedexcept for a plurality of distinct electron emission aperturescommunicating between the cavity and the exterior of said body, acoating of electron emissive material upon the internal surface of saidbody, means for heating said body, a plurality of electron acceleratingelectrodes positioned adjacent said body each aligned with a respectiveone of said apertures, and means for electrically biasing each of saidelectron accelerating electrodes independent of the other of saidelectron accelerating electrodes.

3. An electron discharge device comprising a highly evacuated envelope,a body having a cavity therein mounted within said envelope, a coatingof electron emissive material on the bounding surface of said cavity,said body being closed except for a plurality of apertures communicatingbetween said cavity and the exterior of said body, individual means forindependently controlling the electron beam intensity from each of saidapertures and a heater for said body.

4. An electron discharge device comprising a highly evacuated envelope,a cathode within said envelope com prising a body including a planarwall and having a hemispherical cavity therein adjacent said planarwall, a coat ing of electron emissive material upon the bounding wallsof said cavity, said body being closed except for a plurality ofelectron egress apertures in said planar wall communicating between thecavity and the exterior of said body, electron accelerating means inspaced juxtaposition with said plurality of apertures, and a heater forsaid cathode.

. 5. A high vacuum electron discharge device comprising an envelope, acathode within said envelope comprising a hollow tube which is closedexcept for a plurality of electron egress apertures, a coating ofelectron emissive material upon the inside of said tube, electronaccelerating means in spaced juxtaposition with the plurality ofapertures in said cathode, and means for heating said hollow tube.

6. An electron discharge device comprising a highly evacuated envelope,a hollow cathode cylinder, a coating of electron emissive material uponthe internal surface of said cylinder, said cylinder being closed exceptfor a plurality of apertures in the curved side wall communicatingbetween the interior and exterior of said cylinder, an anodeencompassing said cathode cylinder, and a heater for said cathodecylinder.

7. An electrode assembly for an electron discharge device comprising aconducting body including a cavity therein, a coating of electronemissive material upon the bounding wall of said cavity, said conductingbody being closed except for a plurality of distinct electron egressapertures communicating between the cavity and the exterior of saidbody, a heater for said body, an electron accelerating means spaced fromsaid body, and a modulating electrode positioned between said body andsaid elec tron accelerating means, said electron accelerating means andsaid modulating electrode being aligned with the apertures in said body.

8. An electrode assembly in accordance with claim 7 wherein saidmodulating electrode comprises a plate including apertures correspondingin position to the apertures in said body.

9. An electrode assembly in accordance with claim 8 wherein theapertures in said plate are substantially the same size as the aperturesin said body.

10. An electron discharge device comprising a highly evacuated envelope,a conducting body including a cavity therein mounted within saidenvelope, a coating of electron emissive material upon the internalsurface of said body bounding said cavity, said body including a walldefining a plurality of electron emission apertures communicatingbetween the cavity and exterior of said body, said body being closedexcept for the electron emission apertures in said wall, a heater forsaid body, and electron accelerating means adjacent the wall of saidbody and in juxtaposition with said apertures.

References Cited in the file of this patent UNITED STATES PATENTS1,128,292 Colpitts Feb. 16, 1915 1,280,769 Sangmuir Oct. 8, 19182,026,892 Heintz Jan. 7, 1936 2,125,279 Bieling Aug. 8, 1938 2,201,817Smith May 21, 1940

